1. Technical Field
The present invention relates to a switching power device supplying dc power to an electronic device and, more particularly to a switching power device that can prevent the heat generation and burning of an electronic circuit due to a short-circuit current when the output side of the electronic circuit connected to the switching power device is short-circuited.
2. Description of Related Art
Generally, as power devices of television receivers, video devices, disk devices or the like, many switching power devices are employed. In each of the switching power devices, when the output side of the switching power device is short-circuited owing to any cause, the fall of the output voltage of the switching device is detected to operate a latch circuit and the switching operation of the switching power device is stopped to prevent the switching power device from generating heat and being burnt owing to a short-circuit current. However, when the output side of an electronic circuit such as a three-terminal regulator connected to the output side of the switching power device is short-circuited, the latch circuit does not operate, so that the switching operation of the switching power device is not stopped. Thus, the electronic circuit connected to the output side of the switching power device undesirably generates heat and is burnt due to the short-circuit current.
It is known that when the output side of a switching power circuit is short-circuited, an abnormal fall of a cathode voltage of a rectifying diode in each output side of a secondary side winding of a switching transformer of the switching power circuit is detected to stop the supply of electric current to a primary side winding of the switching transformer of the switching power circuit (for instance, see JP-A-4-251520).
Further, a technique is known that when the output side of a switching power circuit is short-circuited, a voltage abnormality detecting diode connected to the output side of a secondary side winding of a switching transformer is electrically conducted to detect the short-circuit of the output side of the switching power circuit, and output voltage to a primary side winding of the switching transformer of the switching power circuit is suppressed to lower the output voltage of the secondary side winding of the switching transformer (for instance, see JP-A-6-327241).